Introduction:

When a molecule experiences a chemical change, the atoms that made up that molecule are recombined into new molecules. The old molecule is history, although that atoms are still around. In a physical change, the shape or state of the molecule is different, but the original molecule is still intact. Wax gives us a great contrast between the two kinds of change.

Activity:

• You will be given a candle and test tube containing wax. You will use a scale to determine the mass of the candle and the test tube containing wax.
• You will then light the candle and use it to melt the wax in the test tube. Once the wax is completely melted, you will again determine the mass of the candle and the test tube containing wax.
• Get the document B6_MeltingVsBurning from my Teachers Folder. Fill in the data you measured.
• Draw conclusions about the difference between Melting and Burning in the space provided.

Conclusion:

Melting and burning are different things. Although candle wax melts before it burns, it can melt without burning. Burning is a chemical change that results in new molecules, with the fuel and oxygen molecules consumed.

Practice:

The same ideas apply to evaporation. When the dry ice "melted" it went from solid to vapor. Was this a chemical change or a physical change? When a puddle of fuel evaporates off the pavement, is this a chemical change or a physical change? When a waiter ignites a flaming dish, is this a chemical change or a physical change?

Enrichment: